Self-Consistent Effects on the Propagation of Relativistic Runaway Electron Avalanches
Résumé
Terrestrial gamma ray flashes (TGFs) are very short bursts of gamma rays occurring during thunderstorms. They were first reported in 1994 but to this date are still not fully understood. Most detected TGFs seem to be associated with upward negative lightning leaders transporting negative charge upward. It is agreed upon that TGFs are produced by bremsstrahlung emission from energetic electrons created during a phenomenon called Relativistic Runaway Electron Avalanches (RREAs): a relatively high electric field can force high-energy electrons to accelerate continuously and create even more secondary high-energy runaway electrons while partially ionizing the air. However, how such phenomenon establishes itself within the environment of thunderclouds remains up for debate. In recent years, radio emissions over a wide range of frequencies have been observed in association with TGFs. For example, Energetic In-cloud Pulses (EIPs) [e.g., Lyu et al, GRL, 48, e2021GL093627, 2021], slow LF pulses [e.g., Pu et al., GRL, 46, 6990–6997, 2019], and VHF emissions [e.g., Lyu et al, GRL, 45, 2097-2105, 2018]. A better understanding of these radio waves could provide critical information about the mechanisms underlying TGFs. Although relativistic self-consistent modeling of RREAs can provide critical information about the true dynamics of TGFs and the associated radio-emissions, such simulations have not been performed so far. Our work focuses on a relativistic collisional Monte Carlo code coupled with an electromagnetic Particle-In-Cell (PIC) model, used to simulate RREAs and the associated electromagnetic field produced by high- and low-energy particles. With this model, we hope to demonstrate how self-consistent simulations of RREAs constrain the production context of TGFs. In particular, we will focus on the effect of the ambient electric field geometry and the role of charged species.